Staphylococcal Cassette Chromosome Mec Element Research Articles

Diversity of staphylococcal cassette chromosome mec structures in coagulase-negative staphylococci and relationship to drug resistance

The objective of this study was to determine the distribution of staphylococcal cassette chromosome mec (SCCmec) elements in meticillin-resistant coagulase-negative staphylococci (MR-CoNS) isolated from a tertiary-care hospital in Mexico and to examine the relationship to drug resistance. Fifty selected MR-CoNS isolates collected from catheters (n=15), blood (n=15), bone (n=9), bronchial lavage (n=2) and urine (n=2) and one isolate each from an abscess, cerebrospinal fluid, eye, pleural effusion, synovial fluid, tracheal aspirate and wound secretion were examined. Susceptibility testing was performed by the broth microdilution method. SCCmec types were determined by multiplex PCR and PFGE was carried out as described previously for Staphylococcus aureus. Among the MR-CoNS strains studied, the most frequently isolated species were Staphylococcus epidermidis (n=26) and Staphylococcus haemolyticus (n=13). Staphylococcus cohnii (n=5), Staphylococcus hominis (n=3), Staphylococcus sciuri (n=1), Staphylococcus pasteuri (n=1) and the recently described species Staphylococcus pettenkoferi (n=1) were also identified. The most frequent MR-CoNS genotype identified was SCCmec type IVa in S. epidermidis isolates, which also showed a high diversity in their PFGE patterns. A clone was found that amplified both SCCmec III and V elements in five isolates examined. The single MR S. pettenkoferi isolate harboured SCCmec type IVd and the single MR S. pasteuri isolate harboured SCCmec type I. The carriage of SCCmec type III was associated with resistance or intermediate resistance to meropenem (P <0.05). These results confirm the high prevalence of S. epidermidis SCCmec IVa and the high genetic diversity among MR-CoNS strains. As far as is known, this is the first report describing the newly identified S. pettenkoferi possessing SCCmec IVd and S. pasteuri harbouring SCCmec type I. MR-CoNS harbouring SCCmec type III were found to be more resistant to meropenem.

Cooccurrence of Predominant Panton-Valentine Leukocidin-Positive Sequence Type (ST) 152 and Multidrug-Resistant ST 241 Staphylococcus aureus Clones in Nigerian Hospitals

Ninety-six clinical isolates of Staphylococcus aureus from Nigeria were characterized phenotypically and genetically. Twelve multidrug-resistant methicillin (meticillin)-resistant S. aureus (MRSA) isolates carrying a new staphylococcal cassette chromosome mec element and a high proportion of Panton-Valentine leukocidin (PVL)-positive methicillin-susceptible S. aureus (MSSA) isolates were observed. The cooccurrence of multidrug-resistant MRSA and PVL-positive MSSA isolates entails the risk of emergence of a multidrug-resistant PVL-positive MRSA clone.

Epidemiology and susceptibilities of methicillin-resistant Staphylococcus aureus in Taiwan: emphasis on chlorhexidine susceptibility

Chlorhexidine is an antiseptic agent used for hand hygiene worldwide. To evaluate the susceptibility of methicillin-resistant Staphylococcus aureus (MRSA) to chlorhexidine, this study determined MICs of chlorhexidine and another 12 antimicrobial agents, carriage of the Panton–Valentine leukocidin, qacA/B, and smr genes, genetic relatedness by multilocus sequence typing (MLST), and staphylococcal cassette chromosome mec element type for 206 MRSA clinical isolates from the Taiwan Surveillance of Antimicrobial Resistance program III and IV (years 2002 and 2004) from 26 hospitals. Using MLST, we respectively identified 102 (49.5%), 68 (33.0%), 13 (6.3%), 5 (2.4%), 5 (2.4%), and 13 (6.3%) isolates as ST239, ST59, ST5, ST241, ST573, and other types. The MIC 50 and MIC 90 of chlorhexidine for all 206 isolates were 2 and 8 μg/mL, respectively. Seventy-three (35.4%) isolates carried qacA/B gene, but none carried smr. For the 72 (35.0%) MRSA isolates with chlorhexidine MIC ≥4 μg/mL, 53 were ST239 (49 of them carried qacA gene), 12 were ST5 (all carried qacB gene), 5 were ST241 (4 carried qacA gene), 1 was ST338 (and carried qacA gene), and 1 was ST573 (and carried qacA gene). Compared with other sequence-type MRSA isolates, ST239 MRSA isolates were the most resistant to both chlorhexidine and other antimicrobial agents. Methicillin-resistant S. aureus strains with disinfectant resistance qacA/B genes are common in Taiwan. High frequency of qacA/B genes among specific sequence types (ST239, ST5, and ST241) resulted in low susceptibility to chlorhexidine. Periodic surveillance of antiseptic susceptibility among MRSA isolates is important for the control of nosocomial hospital-acquired infections.

A novel type-III staphylococcal cassette chromosomemec(SCCmec) variant among Indian isolates of methicillin-resistantStaphylococcus aureus

We identified a novel type-III staphylococcal cassette chromosome mec (SCCmec) element carried by eight methicillin-resistant Staphylococcus aureus (MRSA) strains from different wards and patients in an Indian hospital. Although the pulsed-field gel electrophoresis pattern and spa types of eight strains were identical and clonally related to other nosocomial Indian isolates that belonged to sequence type (ST) 239 and spa type t037, the minimum inhibitory concentration (MIC) of these eight variants was noticeably low compared with the typical type-III isolates from the same hospital, and we were unable to identify ccrC and hsdR by multiplex PCR, although mer operon and transposases A, B, and C of Tn554 were amplified. By amplifying the entire SCCmec region by long-range PCR and determining parts of the nucleotide sequences of one isolate (V14), we found that the strain carried a novel SCCmec element containing a 422 bp sequence, which is highly homologous to that identified in strain CCR1-9583, mer operon and plasmid pT181 integrated in tandem via IS431 in the J3 region. It also carried a cassette chromosome, previously reported to be an SCC-like element, downstream of type-III SCCmec. Because PCR amplification of representative genes showed that these eight strains carried the same genetic elements, they belong to a novel MRSA clone that differs from most nosocomial clones carrying type-III SCCmec and SCCmercury, despite belonging to the ST239 genotype.

High rates of community-acquired, Panton-Valentine leukocidin (PVL)- positive methicillin-resistant S. aureus (MRSA) infections in adult outpatients in Greece

Staphylococcus aureus was isolated in 88 (30.8%) of 286 adult patients suffering from various skin and soft-tissue infections examined in the outpatient department of a 650 bed tertiary-care hospital of Athens, Greece between January 2006 and December 2007. Twenty-seven (30.7%) of the S. aureus infections were caused by methicillin-resistant S. aureus (MRSA). All MRSA isolates were also resistant to tetracycline, fucidic acid and kanamycin, but were sensitive to gentamicin and tobramycin, as well as to to cotrimoxazole, chloramphenicol, quinolones, clindamycin and erythromycin. All isolates belonged to staphylococcal cassette chromosome mec elements (SCCmec) type IV, and were found to carry the lukF-PV and lukS genes coding for Panton-Valentine leukocidin (PVL). Pulsed-field gel electrophoresis (PFGE) and spa-typing revealed high genetic similarity among all MRSA isolates and with the PFGE pattern of the well-described ST80 clone that seems to be spreading through Europe. The high prevalence of MRSA among S. aureus infections in the community signify that empiric therapy in Greece, when clinically indicated, should exclude beta-lactam antibiotics. Moreover, the establishment of an active screening for PVL-positive community-acquired (CA)-MRSA carriage and the adoption of a search and destroy strategy for CA-MRSA in all patients admitted with purulent skin and soft-tissue is of high priority in Greece as well as in all European countries which face high rates of CA-MRSA infection.

Molecular characterization of methicillin-resistant Staphylococcus epidermidis strains from bacteraemic patients

In order to study the clonality of clinical methicillin-resistant Staphylococcus epidermidis (MRSE) strains and their staphylococcal cassette chromosome mec (SCCmec) elements, 60 isolates of MRSE from bacteraemic patients in three units of the Helsinki University Hospital, Finland were selected, covering the periods 1990-1993 and 1997-1998. The MRSE strains were analysed by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing and SCCmec typing. Eleven PFGE types (FIN-SE-1-11) with sequence type ST2 (clonal complex 2; CC2) were identified. The previously established methicillin-resistant Staphylococcus aureus SCCmec criteria were applied to name the MRSE SCCmec complexes, and it was found that 7% of the isolates carried SCCmec type IA (ccrA1, class B), whereas the majority (93%) yielded six non-typeable SCCmec PCR patterns (P1-P6). Within each SCCmec PCR pattern, two ccr recombinase genes (ccrA2 and ccrA3) and two mec gene complexes (class A and class B) were detected. In addition, the ccrC gene was associated with three of the six patterns. In conclusion, the MRSE strains were genetically related to each other (ST2) but their SCCmec complexes were unique combinations of elements previously recognized among SCCmec types III and IV.

A Case of Perianal Abscess due to Panton-Valentine Leukocidin Positive Community-Associated Methicillin-Resistant Staphylococcus aureus : Report in Korea and Literature Review from the Far East

Submitted 9 December, 2007, accepted 15 February, 2008 This work was supported by the Korea Research Foundation Grant funded by the KoreanGovernment (MOEHRD) KRF-2005-003-E00119. Correspondence:Dong-GunLee, M.D. Department of Internal Medicine, St. Mary’ Hospital #62, Youido-dong, Youngdungpo-Gu, Seoul 150-713, Korea Tel:+82-2-590-2494, Fax:+82-2-535-2494 E-mail:symonlee@catholic.ac.kr (HA-MRSA). The incidence of methicillin resistance among nosocomial isolates of S. aureus is now higher than 60% in Korea (3). Moreover, recent reports have described an increasing incidence of community-associated MRSA (CA-MRSA) in patients who do not exhibit established risk factors for HA-MRSA and it has become a major concern worldwide (2, 4). Some epidemiological studies have suggested that most of CA-MRSA strains had association with lack of multi-drug resistance, predominance of staphylococcal cassette chromosome mec element (SCCmec) IV and high prevalence of Panton-Valentine leukocidin (PVL) 증 례

Variability in SCC mecN1 spreading among injection drug users in Zurich, Switzerland

BackgroundAn extremely low level methicillin resistant Staphylococcus aureus (MRSA) belonging to ST45, circulates among intravenous drug users in the Zurich area. This clone can be misinterpreted as an MSSA by phenotypic oxacillin resistance tests, although it carries a staphylococcal cassette chromosome mec (SCCmec) element encoding a functional mecA gene and it produces PBP2a.ResultsThis clone carried a new 45.7-kb element, termed SCCmecN1, containing a class B mec complex (mecA-ΔmecR1::IS1272), a truncated Tn4003 harbouring the dfrA gene, and a fusB1 gene, conferring methicillin, trimethoprim and low level fusidic acid resistance, respectively. In addition to the two insertion site sequences (ISS) framing the SCCmec, a third ISS (ISS*) was identified within the element. SCCmecN1 also harboured two distinct ccrAB complexes belonging to the class 4 subtype, both of which were shown to be active and to be able to excise the SCCmecN1 or parts thereof. Slight variations in the SmaI-PFGE pattern of the clinical MRSA isolates belonging to this clone were traced back to differences in the sizes of the SCCmec J2 regions and/or to a 6.4-kb deletion extending from ISS* to the right end ISS. This latter deletion led to a variant right SCCmec-chromosomal junction site. MRSA clones carrying the shorter SCCmec with the 6.4-kb deletion were usually ciprofloxacin resistant, while strains with the complete SCCmecN1 were co-trimoxazole resistant or had no additional resistances. This suggested that the genetic backbone of the host S. aureus, although identical by PFGE pattern, had at some stage diverged with one branch acquiring a sulfonomide resistance mutation and the other ciprofloxacin resistance.ConclusionThis description of the structure and variations of SCCmecN1 will allow for quicker and easier molecular detection of this clone and monitoring of its spread.

Staphylococcal Cassette Chromosomemecin MRSA, Taiwan

To determine the predominant staphylococcal cassette chromosome (SCC) mec element in methicillin-resistant Staphylococcus aureus, we typed 190 isolates from a hospital in Taiwan. We found a shift from type IV to type III SCCmec element during 1992–2003, perhaps caused by selective pressure from indiscriminate use of antimicrobial drugs.

Characterization of methicillin-resistant Staphylococcus aureus from Ulaanbaatar, Mongolia

In order to expand current knowledge of the types of methicillin-resistant Staphylococcus aureus (MRSA) strains circulating in central Asia, six MRSA strains collected from hospitals in Ulaanbaatar, Mongolia during 2000-2002 were examined. Three strains possessed a staphylococcal cassette chromosome mec (SCCmec) element of type IV c, were sequence type (ST) 154 according to multilocus sequence typing (MLST), and contained lukS-lukF (Panton-Valentine leukocidin). Another three strains contained a SCCmec element of type III and were MLST type ST 239. Using automated ribotyping, the six MRSA strains were divided into four different EcoRI ribotypes, and two groups of isolates were distinguished by means of SmaI-macrorestriction patterns. In comparison to other countries, the incidence of MRSA in Mongolia is low.

Le staphylocoque doré résistant à la méticilline : émergence et bases moléculaires de la résistance

Methicillin-resistant Staphylococcus aureus (MRSA) is often the severe causal agent in nosocomial infections that are becoming increasingly difficult to cure because of emerging resistance to all current antibiotic classes. Geographic spread of several MRSA clones between countries and continents has been reported and proven by molecular evidence. Several strains have been isolated from patients in the community without established risk factors for MRSA acquisition. Some of them may have origins in the hospital but others appear to be community-acquired strains. Community MRSA strains have several distinguishing characteristics that may enable them to more readily colonize and infect otherwise healthy hosts. Molecular typing approaches have been used with great advantage in studying of the MRSA epidemiology. It appears that a complete characterization of MRSA requires not only identification of the genetic background of the bacteria but also identification of the structural types of Staphylococcal Cassette Chromosome mec element (SCC mec), which carries methicillin resistance determinant mecA. Rapid and precise identification of MRSA is a prerequisite for control of hospital infections. This article reviews recent publications addressing the epidemiology markers of MRSA, specially of community-acquired strains, and the genetic diversity of SCC mec for identifying MRSA. It appears that MRSA will be an increasing important pathogen in the community.

Severe Staphylococcus aureus infections caused by clonally related community-acquired methicillin-susceptible and methicillin-resistant isolates.

We investigated the genetic relatedness of 5 community-acquired (CA) Staphylococcus aureus isolates obtained from 4 consecutive pediatric patients presenting with sepsis syndrome and severe pneumonia during a 3-week period in 2000. Two patients were infected with methicillin-susceptible S. aureus (MSSA), and 2 were infected with methicillin-resistant S. aureus (MRSA). The pulsed-field gel electrophoresis patterns for the 2 CA-MRSA isolates were identical to each other, as were the patterns for the 3 CA-MSSA isolates. A 2-band difference reflecting the presence of a staphylococcal cassette chromosome mec (SCCmec) element distinguished the CA-MRSA isolates from the CA-MSSA isolates. The small, mobile type IV SCCmec element was present in the CA-MRSA isolates. These data suggest that an insertion or, less likely, a deletion of the SCCmec type IV element occurred in a highly virulent S. aureus background. Staphylococcal toxin genes sea, seh, lukS-PV, and lukF-PV were detected in all isolates. Also, in all isolates, was a partial homolog of seo (seo'). The relationship among these patient isolates strengthens the assumption that CA-MRSA infections may be caused by isolates closely related to MSSA isolates.

Comparative molecular analysis of community- or hospital-acquired methicillin-resistant Staphylococcus aureus.

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is a growing public health concern that has been associated with pediatric fatalities. It is hypothesized that the evolution of CA-MRSA is a recent event due to the acquisition of mec DNA by previously methicillin-susceptible strains that circulated in the community. This study investigated the genetic relatedness between CA-MRSA, hospital-associated MRSA (HA-MRSA), and nonmenstrual toxic shock syndrome (nmTSS) isolates. Thirty-one of 32 CA-MRSA isolates were highly related as determined by pulsed-field gel electrophoresis and spa typing yet were distinguishable from 32 HA-MRSA strains. The 31 related CA-MRSA isolates produced either staphylococcal enterotoxin B (n = 5) or C (n = 26), and none made TSS toxin 1. All CA-MRSA isolates tested contained a type IV staphylococcal cassette chromosome mec (SCCmec) element. In comparison, none of the HA-MRSA isolates (n = 32) expressed the three superantigens. Antibiotic susceptibility patterns were different between the CA-MRSA and HA-MRSA isolates; CA-MRSA was typically resistant only to beta-lactam antibiotics. Six of twenty-one nmTSS isolates were indistinguishable or highly related to the CA-MRSA isolates. MnCop, an nmTSS isolate obtained in Alabama in 1986, was highly related to the CA-MRSA isolates except that it did not contain an SCCmec element. These data suggest that CA-MRSA strains may represent a new acquisition of SCCmec DNA in a previously susceptible genetic background that was capable of causing nmTSS. CA-MRSA poses a serious health risk not only because it is resistant to the antibiotics of choice for community-acquired staphylococcal infections but also because of its ability to cause nmTSS via superantigen production.

Exposure of the arsenal of another human pathogen

Staphylococcus aureus is an important opportunistic Gram-positive bacterial pathogen that can cause a variety of both hospital- and community-acquired infections in humans. The recent emergence of strains that are resistant to all antibiotics in use, including the last ‘magic bullet’ vancomycin, coupled with the lack of an effective anti-staphylococcal vaccine, has made this pathogen a major health concern. Thus, a better understanding of the biology and pathogenicity of S. aureus is crucial for the discovery of novel targets for antimicrobial agent and vaccine development. With this in mind, the recent publication of the whole genome sequences of two related methicillin-resistant strains of S. aureus (N315 and Mu50) by Kuroda et al.1xWhole genome sequencing of methicillin-resistant Staphylococcus aureus. Kuroda, M. et al. Lancet. 2001; 357: 1225–1240Abstract | Full Text | Full Text PDF | PubMed | Scopus (1140)See all References1 has been hailed with much enthusiasm.The circular chromosomes of strains N315 and Mu50 are ∼2.8 Mb in size, have a low G+C content (∼33%), and are predicted to contain 2595 and 2697 ORFs, respectively. The nucleotide sequences of the two genomes are 96% identical, most of the differences being caused by the presence of Mu50-specific mobile genetic elements. S. aureus is grouped with Bacillus spp. on the basis of rRNA sequence. Consistent with this, up to 52% of the predicted proteins of N315 are most similar to those from B. subtilis and Bacillus halodurans. These proteins are mostly involved in essential cellular functions. The remaining predicted proteins are encoded by a complex mixture of genes, many of which might have been acquired by lateral gene transfer.The N315 and Mu50 genomes both contain numerous mobile genetic elements, including insertion sequence (IS) elements, transposons, prophages and pathogenicity islands. Many of these elements carry drug resistance and other virulence determinants (such as toxin genes), having important implications for the lateral spread of these factors. Indeed, the plasticity of the S. aureus genome is crucial for the ability of this pathogen to adapt and respond to the selective pressures of its environment.A future challenge lies in the dissection of the molecular basis of high β-lactam resistance and vancomycin resistance in S. aureus. N315 and Mu50 contain a virtually identical mobile staphylococcal cassette chromosome mec (SCCmec) element that encodes resistance to β-lactams and several other antibiotics. N315 exhibits only low-level β-lactam resistance, whereas Mu50 exhibits high-level β-lactam and vancomycin resistance. However, it is possible to isolate N315 derivatives with high-level β-lactam or vancomycin resistance in vitro using a two-step selection process. Given the genetic relatedness of N315 and Mu50, a detailed comparison of the genome sequences of these strains, coupled with gene expression studies, should shed light on the molecular mechanisms responsible for these conversions.Genes encoding almost all of the previously identified virulence factors of S. aureus are present in both genomes. Furthermore, 70 new putative virulence factors were identified, highlighting the remarkable pathogenic potential of this bacterium. As many as 18 predicted proteins were identified that contain a carboxy-terminal LPXTG motif, typical of many cell wall-anchored proteins of Gram-positive bacteria. Of these, seven are previously identified adhesins. In addition, the genes encoding 22 putative exoenzymes, six of which are new candidates, were identified. Interestingly, both N315 and Mu50 appear to have the capability to produce numerous proteins that target the host immune response. These include an impressive array of secreted exotoxins and enterotoxins with superantigen activity, the genes for which are clustered into three pathogenicity islands. Furthermore, genes encoding four MHC class II β-chain analogues were also identified. Three of these predicted proteins are similar to the previously identified Map protein of S. aureus, which binds to a variety of host extracellular matrix molecules and which might also have immunomodulatory activity.